You feel it as a slight shaking, a side-to-side motion that is over before you realise what it was. Your hands grab for support and you brace yourself for what might come. Nothing happens, you breathe out and life goes on as before.
Some liken the tremors still rumbling through north-western Turkey to the roll of a rough boat ride, or the feeling of space-walking some get from taking the controversial anti-malaria drug Lariam.
Most frighteningly, the building cracks and groans, and then readjusts itself. In the silence that follows, your mind empties itself of all the useless junk that normally resides there. Only essential thoughts remain - of friends, family, survival, and death.
The continuing after-shocks are mere ripples compared to the massive jolt experienced early last Tuesday morning. But for those who lived through the original nightmare, each tremor holds out the threat of new horrors.
Fear of a recurrence is making sleepless zombies of the inhabitants of Istanbul and other towns in the region. Even "the lucky ones" who survived with their houses, their possessions or just their lives are reliving the misery of the quake over and over again.
Most have lost all faith in the power of their homes to withstand further tremors. Many have taken up residence in the city's squares and parks, or anywhere they can find in this crowded and usually noisy city.
Logic is not a feature of their behaviour. They spend the day indoors, but every evening the exodus to the open starts afresh. The moment everyone most fears is 3.02 a.m., the exact time the quake struck last Tuesday.
People know there is no pattern to earthquake activity, but no one wants to live through another tremor during the night. Many survivors woke to last week's quake to find their bedrooms rocking and crumbling, and all electric power gone. Sleep-heavy and in total darkness, they rounded up their families and fumbled their way to safety.
In the muggy heat of late August, the rich have taken flight to holiday resorts to the south. The rest of the city's inhabitants have no such luxury.
Mass terror reached its height last Thursday when at least 2 million stayed outdoors for the entire evening. Restaurants, cafes and shops closed early - there were no customers anyway - and thousands flocked to Taksim Square and other large plazas not hemmed in by surrounding buildings.
Even the city's governor declared his intention to sleep alfresco, after Turkey's national earthquake observatory warned of the possibility of further big tremors. But just like last week, when it underestimated the scale of the quake, the local experts were wrong again, and nothing happened.
It is only foreigners who, by and large, ignore the paranoia and sleep in their beds. Ignorant of the general mood, or unwilling to give up their comforts, they have remained in their apartments. The lure of air-conditioned hotels and sprung mattresses was simply too great for most visitors (including this one). They had company in the head of the Eastern Orthodox Church, Patriarch Bartholomew. Asked on Thursday where he would sleep, the spiritual leader of the world's 300 million Orthodox Christians (of which only 4,000 remain in Istanbul), is reported to have said: "In my bed, of course. I don't move for the Earth. It moves for me."
Tourists are thin on the ground anyway. Istanbul's sights, such as the Blue Mosque, the Aya Sofya and Topkapi, were virtually deserted at the weekend. For Turkey's £5 billion a year tourism industry, things are going from bad to worse this year. An air of general depression lingers. Everyone knows people who have died or lost homes in the disaster, and many busy themselves with quixotic expeditions to bring relief to the hardest-hit areas.
In all the chaos and devastation, only the city's army of shoe-shine boys, legless beggars and other homeless have remained unaffected. For once, not having a roof over your head has proved something of a blessing.